1. Field of the Invention
Embodiments of the present patent application generally relate to an image forming apparatus including an image processing member, and more particularly, to an image forming apparatus including an image processing member such as a photoconductor, a cleaning blade, a toner collection roller, and a developing roller, and employing a method of evaluating a distribution of adhesion forces of toner to the image processing member and powder removability indicating a degree of difficulty of removing powder particles from the image processing member.
2. Discussion of the Related Art
Related-art image forming apparatuses generally include image forming components such as a photoconductor, a developing unit, and a cleaning unit. The cleaning unit includes a cleaning blade and/or a cleaning brush to clean a surface of the photoconductor by removing toner adhering to the surface thereof.
Consequently, related-art cleaning methods of removing toner adhering to a surface of a photoconductor include brush-type cleaning, blade-type cleaning, and the like.
A known cleaning unit that employs brush-type cleaning includes a cleaning brush and a toner collection roller. The cleaning brush is disposed in contact with a surface of a photoconductor to scrape and remove toner from the surface of the photoconductor, and the toner collection roller serves as a cleaning member and is disposed in contact with the cleaning brush to collect the toner therefrom. Further, the toner collected by the toner collection roller is removed from a surface thereof by a cleaning blade that is disposed in contact with the toner collection roller. Since the cleaning blade removes the toner from the surface of the toner collection roller, the toner collection roller can remain clean and therefore can prevent a reduction of toner collection performance from the cleaning brush.
Another known image forming apparatus minimizes a friction coefficient between a surface of a photoconductor and a cleaning member such as a cleaning blade or a cleaning brush, so that such cleaning member can effectively remove toner from the surface of the photoconductor.
Thus, for example, a known toner collection roller has a surface with a friction coefficient smaller than a given friction coefficient so that toner can be effectively removed from the surface of the toner collection roller. The smaller friction coefficient of the surface of the toner collection roller prevents the cleaning blade from curling upon contact with the toner collection roller, thereby preventing a gap from forming between the cleaning blade and the toner collection roller through which toner might otherwise slip or fall. Therefore, the smaller friction coefficient of the surface of the toner collection roller can lead to more effective toner collecting performance or cleaning performance.
However, when actual cleaning performance of the toner collection roller was examined, the inventors of the present patent application often found that, even though the friction coefficient of the surface of the toner collection roller was small, the toner could not be removed from the surface of the toner collection roller effectively. Because of the above-described result, the inventors found that it was difficult to fully rely on a method of evaluating the performance of collecting the toner from the surface of the toner collection roller based on the friction coefficient.
On the other hand, some methods of measuring adhesion forces generated between a powder and a member, i.e., an image processing member, have been proposed. In one method, for example, adhesion forces between an image processing member and one PMMA (polymethylmethacrylate) particle having a composition, particle diameter, and shape similar to those of a toner particle are measured by using an atomic force microscope or AFM.
The measured adhesion forces between the powder particle and the image processing member represent a characteristic value indicating a contact condition of the powder particle and the image processing member. Thus, whether or not the powder can be effectively removed from the image processing member can be evaluated based on measurements of the adhesion forces between the powder particle and the image processing member.
However, when the above-described evaluation is performed based on the thus-measured adhesion forces, it is likely to cause the following problems, details of which are described with reference to FIGS. 1 and 2.
FIG. 1 is a graph showing measurements of adhesion forces that are generated between the surfaces of image processing members A and B and a power particle taken at multiple points on the surfaces thereof. FIG. 2 is a graph showing measurements of adhesion forces that are generated between a powder particle and the surfaces of the image processing member A and of an image processing member C, which is different from the image processing members used in the test having the results shown in the graph of FIG. 1, taken at multiple points on the surfaces thereof. In FIGS. 1 and 2, the horizontal axis of each graph indicates adhesion force between a powder particle and an image processing member, and the vertical axis indicates frequency of powder per specific adhesion forces.
Both image processing members A and B in FIG. 1 have frequencies in proximity to respective mean values of adhesion forces measured at the above-described multiple points, and the results thereof form respective graphs with a sharp peak in the center. That is, most adhesion forces of toner are plotted close to the respective mean values of the adhesion forces of toner to the members A and B, and therefore are significantly correlated when the mean value of the adhesion forces of toner is substituted for the adhesion force.
The mean value of the adhesion force of toner to the image processing member A, which is represented by “x” indicated with a dashed-dotted line, and the mean value of the adhesion force of toner to the image processing member B, which is represented by “y” indicated with another dashed-dotted line, are different. That is, the mean value of the adhesion force “y” is greater than the mean value of the adhesion force “x”, which shows that the image processing member B has a greater mean value of the adhesion forces than the image processing member A. At the same time, it is easily expected that the cleaning performance of the image processing member B is poorer than the cleaning performance of the image processing member A. For example, when with the adhesion forces smaller than an adhesion force “z” shown in FIG. 1 one can perform good cleaning and with the adhesion forces greater than the adhesion force “z” one cannot remove toner effectively from the image processing member A, it can be foreseen that the toner on the overall surface of the image processing member A may be removable whereas the toner on the surface of the image processing member B may not.
In FIG. 2, the image processing member B is replaced by the image processing member C to show results of comparison of the adhesion forces of toner to the image processing member A and adhesion forces of toner to the image processing member C. As shown in FIG. 2, a frequency distribution of adhesion forces of toner to the image processing member C is much more evenly distributed, or gentle curved or sloped, than a frequency distribution of adhesion forces of toner to the image processing member A, while the mean value of the adhesion force thereof is same as the image processing member A, and therefore is indicated by “x.”
In other words, although the mean value of the adhesion force of toner to the image processing member C is substantially the same as the mean value of adhesion forces of toner to the image processing member A, at any given portion on the surface of the image processing member C the adhesion forces of toner to the image processing member C may be greater or smaller than those of the image processing member A. For example, even when the mean value of the adhesion forces of toner to the image processing member C is equal to or smaller than the adhesion force “z”, the adhesion forces beyond the adhesion force “z” of toner to the image processing member C may be greater than the image processing member A at some portions on the image processing member C. Therefore, even when most toner can be removed from the image processing member C, some amount of toner still remains at some portions on the image processing member C.
Therefore, even when the degree of toner adhesion to a member such as the image processing member C having the above-described tendency of toner adhesion is evaluated based on the mean value of the adhesion forces and it is determined that the image processing member C has good toner cleaning performance, some toner can still remain on the surface of the image processing member C without being removed effectively.
It is therefore important to determine in advance whether the adhesion force is equal at any portion on a surface of an image processing member to which toner adheres, in other words, evaluate a distribution of adhesion forces of toner to an image processing member.
Further, the above-described problems may arise not only with the toner collection roller but also with any image processing member to which toner adheres in an image forming apparatus, for example, a photoconductor or a developing member. That is, the above-described problems may occur at any portion where a powder particle moves from one member to another.
A description is given of example problems that can arise with a developing member such as a developing roller.
A related-art developing unit that generally develops a latent image into a visible toner image with, for example, one-component developer including toner, is known to include a developing roller, a developer regulating member, and a developer supplying roller. The developing roller is disposed facing a photoconductor of an image forming apparatus.
The one-component developer or toner contained in the related-art developing unit is supplied to the developing roller while the toner is frictionally charged appropriately by sliding contact with the developing roller and the developer supplying roller. The toner carried on the surface of the developing roller is regulated by the developer regulating member to form a uniform thin layer and, at the same time, is supplied with a given electrical charge. The photoconductor and the developing roller form a development area where the toner on the surface of the developing roller is attracted by a development electrical field and transferred to a latent image formed on the photoconductor to develop the latent image into a visible toner image.
Residual toner that remains on the surface of the developing roller without being used in the development area is collected by the developing roller at a contact point where the developing roller contacts the developer supplying roller. At the same time, with the rotation of the developer supplying roller, new or unused toner is supplied to the surface of the developing roller. In addition, the toner collected by the developer supplying roller is mixed with toner contained in the developing unit by the rotation of the developer supplying roller for eventual reuse.
Such residual toner that has not been used for image forming remains on the surface of the developing roller may be subjected to significant repetitive stress and may deteriorate, losing its toner charge property. Further, such toner deterioration can easily cause so-called toner filming on the surface of the developing roller. The toner filming may prevent providing and maintaining good charging performance on the surface of the developing roller, which may result in a significant adverse affect on image formation.
Therefore, it is important to determine in advance the distribution of adhesion forces of toner to the surface of the developing roller with respect to the toner, so that the developer supplying roller can effectively collect the toner remaining on the surface of the developing roller at any point on the surface of the developing roller.